Relationship between indoor and outdoor bio-aerosols collected with a button inhalable aerosol sampler in urban homes

This field study investigated the relationship between indoor and outdoor concentrations of airborne actinomycetes, fungal spores, and pollen. Air samples were collected for 24 h with a button inhalable aerosol sampler inside and outside of six single-family homes located in the Cincinnati area (overall, 15 pairs of samples were taken in each home). The measurements were conducted during three seasons - spring and fall 2004, and winter 2005. The concentration of culturable actinomycetes was mostly below the detection limit. The median indoor/outdoor ratio (I/O) for actinomycetes was the highest: 2.857. The indoor of fungal and pollen concentrations followed the outdoor concentrations while indoor levels were mostly lower than the outdoor ones. The I/O ratio of total fungal spores (median=0.345) in six homes was greater than that of pollen grains (median=0.025). The low I/O ratios obtained for pollen during the peak ambient pollination season (spring) suggest that only a small fraction penetrated from outdoor to indoor environment. This is attributed to the larger size of pollen grains. Higher indoor concentration levels and variability in the I/O ratio observed for airborne fungi may be associated with indoor sources and/or higher outdoor-to-indoor penetration of fungal spores compared to pollen grains. Practical Implication This study addresses the relationship between indoor and outdoor concentrations of three different types of bio-aerosols, namely actinomycetes, fungal spores, and pollen grains. The results show that actinomycetes are rare in indoor and outdoor air in Midwest, USA. Exposure to pollen occurs mainly in the outdoor air even during peak pollen season. Unexpectedly high fungal spore concentrations were measured outdoors during winter. The presented pilot database on the inhalable levels of indoor and outdoor bio-aerosols can help apportion and better characterize the inhalation exposure to these bio-aerosols. Furthermore, the data can be incorporated into existing models to quantify the penetration of biological particles into indoor environments from outdoors.     

Assessment of airborne bacteria and fungi in food courts

A study was undertaken to determine the effect of variations in temperature, relative humidity, occupancy density and location (indoor/outdoor) on the concentrations of viable airborne bacterial and fungal spores at an air-conditioned and a non air-conditioned food stall in Singapore. Typically, bioaerosols consisted of 50.5% bacteria and 49.5% fungi in the indoor environment. In contrast, for the outdoor environment, bacteria on an average only accounted for 20.6% of culturable airborne microorganisms whereas fungal concentrations were 79.4%. Results on bioaerosol size distributions revealed that 67% of indoor bacteria and 68% of outdoor bacteria, 85% of indoor fungi and 68% of outdoor fungi were associated with fine mode particulates (<3.3 μm). Occupant density was the key factor that affected indoor airborne bacteria concentrations while concentrations of outdoor airborne bacteria depended strongly on ambient temperature. Indoor fungal concentration was positively correlated to relative humidity whereas outdoor fungal concentration was positively correlated to relative humidity and negatively correlated to temperature. The study also compared the biological air quality between a non air-conditioned food stall (Stall A) and an air-conditioned food stall (Stall B). The dining area of the former had lower bacterial concentrations as compared to the latter, while fungal spore’s concentrations showed a reverse trend. The dominant airborne bacteria genera were Staphylococcus, Pseudomonas, Alcaligens, and Corynebacterium whereas Penicillium, Aspergillus and Cladosporium were the most common fungal genera and groups in both food stalls.     

Use of temporal/seasonal- and size-dependent bioaerosol data to characterize the contribution of outdoor fungi to residential exposures

With the use of published temporal/seasonal and particle size distribution of outdoor bioaerosol data and meteorological information in the subtropical climate, we characterized the airborne fungal concentration indoor/outdoor/personal exposure relationships in a wind-induced naturally ventilated residence. We applied a size-dependent indoor/outdoor ratio model coupled with a compartmental lung model based on a hygroscopic growth factor as a function of relative humidity on aerodynamic diameter and concentration of fungal spores. The higher indoor airborne fungal concentrations occurred in early morning and late afternoon in which median values were 699.29 and 626.20 CFU m(-3) in summer as well as 138.71 and 99.01 CFU m(-3) in winter, respectively, at 2 am and 8 pm. In the absence of indoor sources, summer has higher mean indoor/outdoor ratios of airborne fungal concentration (0.29-0.58) than that in winter (0.12-0.16). Lung region of extrathoracic (ET) has higher fungal concentration lung/indoor ratios (0.7-0.8) than that in bronchial (BB; 0.41-0.60), bronchiolar (bb; 0.12-0.40), and alveolar-interstitial (AI); 0.01-0.24) regions. The highest airborne fungal deposition dose (95th-percentile is 4600 CFU) occurred in 11 pm-5 am in region AI in that the 95th-percentile fungal deposition rate was 0.22 CFU s(-1).     

Fungal aerosol composition in moldy basements

Experimental aerosolization studies revealed that fungal fragments including small fragments in the submicrometer size are released from fungal cultures and have been suggested to represent an important fraction of overall fungal aerosols in indoor environments. However, their prevalence indoors and outdoors remains poorly characterized. Moldy basements were investigated for airborne fungal particles including spores, submicron fragments, and larger fragments. Particles were collected onto poly‐L‐lysine‐coated polycarbonate filters and qualitatively and quantitatively analyzed using immunogold labeling combined with field emission scanning electron microscopy. We found that the total fungal aerosol levels including spores, submicrometer, and larger fragments in the moldy basements (median: 80 × 10³ m^?3) were not different from that estimated in control basements (63 × 10³ m^?3) and outdoor (90 × 10³ m^?3). However, mixed effect modeling of the fungal aerosol composition revealed that the fraction of fragments increased significantly in moldy basements, versus the spore fraction that increased significantly in outdoor air. These findings provide new insight on the compositional variation of mixed fungal aerosols in indoor as compared to outdoor air. Our results also suggest that further studies, aiming to investigate the role of fungal aerosols in the fungal exposure‐disease relationships, should consider the mixed composition of various types of fungal particles.     

Characteristics of indoor and outdoor airborne fungi at suburban and urban homes in two seasons

Literature has suggested association between damp environments, microbial exposure, and higher prevalence of respiratory symptoms and diseases. The study began by evaluating the airborne fungal concentrations at urban and suburban areas of a typical metropolitan city in southern Taiwan for the estimation of related health risks. A group of representative homes, based on the housing characteristics questionnaires completed earlier, were selected from two parts of the city; urban and suburban. Burkard sampler (BURKARD, Rickmansworth, England) was used to collect airborne fungi onto agar plates with malt-extract. After incubation and identification, concentrations of airborne fungi were calculated as CFU/m3. The geometric mean (GM) concentration for indoors was 8946 (4372-18,306) CFU/m3 in winter and 4381 (1605-11,956) in summer. For outdoors, it was 11,464 (5767-22,788) CFU/m3 in winter and 4689 (1895-11,603) in summer. In summer, the total fungal concentration, both indoors and outdoors of suburban homes, were significantly higher than those of urban homes. The dominant fungi contributing to such a difference were indoor Cladosporium spp. and outdoor Penicillium spp. (P < 0.01). The indoor/outdoor ratio (I/O) was similar in two areas except for Penicillium spp. in winter and Aspergillus spp. in summer; both higher in the suburban area. Significantly higher levels of airborne fungi were observed in this region than those seen in northern Taiwan or other parts of the world. Future investigations are needed to further examine the effects of these exposures on the related health problems.     

Concentration and size distribution of bioaerosols in an outdoor environment in the Qingdao coastal region

Bioaerosol particles in the atmosphere were collected from the coastal region of Qingdao from Jul. 2009 to Jun. 2010. The concentrations of microorganisms (including culturable, nonculturable, terrestrial and marine microorganisms) were measured. Average concentrations of airborne terrestrial bacteria, marine bacteria, terrestrial fungi, marine fungi and total bioaerosol were in the ranges of 33-664 CFU/m³, 63-815 CFU/m³, 2-777 CFU/m³, 66-1128 CFU/m³ and 85,015-166,094 Cells/m³, respectively. The nonculturable microbes accounted for 99.13% of the total microbes. In addition, there were more culturable marine microbes than culturable terrestrial microbes, and more airborne fungi than bacteria. The concentration of airborne bacteria showed a skewed distribution pattern, while unimodal size distributions were observed for the concentrations of fungi and total microbes. The airborne microbes mainly existed in > 2.1 μm coarse particles. Pearson correlation analysis between the concentrations and meteorological parameters showed that the meteorological parameters had different effects on different kinds of microbes. Sandstorms increased the concentrations of both culturable microbes and total microbes in the bioaerosol.     

Indoor Environmental Risk Factors for Respiratory Health in Children

Abstract The indoor environment of 80 houses in the Latrobe Valley, Victoria, Australia was assessed during six visits performed bi-monthly over a period of one year. Children between 7 and 14 years of age residing in the houses were included, resulting in 148 study children, 53 of whom were asthmatic. A respiratory health questionnaire was completed and skin prick tests performed. Significant risk factors for asthma were: exposure to a gas stove (OR=3.15, 95% CI 1.28-7.72), and indoor pets (OR = 2.68, 95% CI 1.07-6.70). Exposure to airborne Aspergillus spores (+10 CFU/m³, OR=1.51, 95% CI 1.05-2.18) was a risk factor for atopy, while exposure to a gas stove (OR=2.32, 95% CI 1.04-5.18) was a risk factor for respiratory symptoms. In conclusion, exposure to gas stoves, fungal spores and pets in the home were identified as statistically significant risk factors for respiratory health in children.     

Indoor exposure levels of bacteria and fungi in residences,schools, and offices in China: A systematic review

Microbes in buildings have attracted extensive attention from both the research community and the general public due to their close relationship with human health. However, there still lacks comprehensive information on the indoor exposure level of microbes in China. This study systematically reviews exposure levels, the community structures, and the impact factors of airborne bacteria and fungi in residences, schools, and offices in China. We reviewed the major literature databases between 1980 and 2019 and selected 55 original studies based on a set of criteria. Results show that the concentration of indoor bacteria varies from 72.5 to 7500 CFU/m³, with a median value of 1000 CFU/m³, and the concentration of fungi varies from 12 to 9730 CFU/m³, with a median value of 526 CFU/m³. The concentration level of microbes varies in different climate zones, with higher bacterial concentrations in the severe cold zone, and higher fungal concentrations in the hot summer and warm winter zone. Among different buildings, classrooms have the highest average bacteria and fungi levels. This review reveals that a unified assessment system based on health effects is needed for evaluating the exposure levels of bacteria and fungi.     

Airborne endotoxin concentrations in indoor and outdoor particulate matter and their predictors in an urban city

Endotoxins are an important biological component of particulate matter and have been associated with adverse effects on human health. There have been some recent studies on airborne endotoxin concentrations. We collected fine (PM_2.5) and coarse (PM_10‐2.5) particulate matter twice on weekdays and weekends each for 48 hour, inside and outside 55 homes in an urban city in Japan. Endotoxin concentrations in both fractions were measured using the kinetic Limulus Amebocyte Lysate assay. The relationships between endotoxin concentrations and household characteristics were evaluated for each fraction. Both indoor and outdoor endotoxin concentrations were higher in PM_2.5 than in PM_10‐2.5. In both PM_2.5 and PM_10‐2.5, indoor endotoxin concentrations were higher than outdoor concentrations, and the indoor endotoxin concentrations significantly correlated with outdoor concentrations in each fraction (R²=0.458 and 0.198, respectively). Indoor endotoxin concentrations in PM_2.5 were significantly higher in homes with tatami or carpet flooring and in homes with pets, and lower in homes that used air purifiers. Indoor endotoxin concentrations in PM_10‐2.5 were significantly higher in homes with two or more children and homes with tatami or carpet flooring. These results showed that the indoor endotoxin concentrations were associated with the household characteristics in addition to outdoor endotoxin concentrations.     

Profiles and seasonal distribution of airborne fungi in indoor and outdoor environments at a French hospital

A one-year prospective survey of fungal air contamination was conducted in outdoor air and inside two haematological units of a French hospital. Air was sampled with a portable Air System Impactor. During this period of survey, the mean viable fungal load was 122.1 cfu/m³ in outdoor air samples, and 4.1 and 3.9 cfu/m³ in samples from adult and pediatric haematology units, respectively. In outdoor samples, Cladosporium was the dominant genus (55%) while in the clinical units, Penicillium sp. (23 to 25%), Aspergillus sp. (15 to 23%) and Bjerkandera adusta (11 to 13%) were the most frequently recovered airborne fungi. The outdoor fungal load was far higher in autumn (168 cfu/m³), spring (110 cfu/m³) and summer (138 cfu/m³) than in winter (49 cfu/m³). In indoor air, fungal concentrations were significantly lower in winter (2.7 to 3.1 cfu/m³) than in summer (4.2 to 5.0 cfu/m³) in both haematology units. In the outdoor environment, Penicillium sp. and Aspergillus sp. were more abundant in winter while the levels of Cladosporium were lowest during this season. In the haematological units, the presence of Aspergillus sp. was stable during the year (close to 20%), Bjerkandera sp. was particularly abundant in winter (close to 30%); levels of Penicillium sp. were highest in autumn while levels of Cladosporium sp. were highest in spring and summer.     

Study of bio-aerosols in a prominent temple in Mumbai City,India

Numerous health complaints occur with respect to indoor air quality and scanty information is available on the air flora, particularly with respect to bio-aerosols in India. This paper reports a study which examined air quality in a prominent temple in the city of Mumbai. It was found that the indoor microbial load was significantly higher probably because appropriate ventilation systems were lacking. In the festive month of September, the highest bacterial counts (13.98 × 10⁴ CFU/m³) and fungal counts (9.22 × 10⁴ CFU/m³) were observed. Pseudomonas spp. and Aspergillus spp. were found to be predominant in the air microflora sampled. Correlation analysis with meteorological factors such as temperature, relative humidity and wind speed showed that these were non-significant. The study indicated that poor ventilation, number of occupants and their activities in a given area are largely responsible for the variation in microbial loads observed. The data generated underline the question of monitoring crowded areas including places of religious importance. Some remedial measures are suggested.     

Culturable and Total Fungi in Dust Accumulated in Air Ducts in Single-Family Houses

Abstract Fungal spore content in dust accumulated in air ducts was investigated in 24 mechanically ventilated single-family houses of which 15 had also a central air heating system. Dust was collected from the ducts simultaneously with cleaning of the ventilation systems. Besides spore concentrations and flora of culturable fungi, total fungal spore concentrations were determined in dust samples by the aqueous two-phase technique and spore counting with epifluorescence microscopy. Culturable spore concentrations in the dust varied from 10⁴ to 10⁷ CFU/g and total spore concentrations from 107 to 108 spores/g. Total spore concentrations in the duct dust were significantly higher in the air heated houses than in the other mechanically ventilated houses. The difference resulted mainly from a higher proportion of recirculation air and a higher age of the air heated houses. Cladosporium, Penicillium, Aspergillus and yeasts consisted of >90% of fungal flora in the dust. Although total spore concentrations were at the same level both in the exhaust and in the supply ducts in both types of house, culturable fungal spore concentrations were slightly higher in the exhaust ducts than in the supply ducts. The proportion of culturable spores was <5% of total spores in dust accumulated in the ducts.     

Exposure to culturable airborne bioaerosols during noodle manufacturing in central Taiwan

Biological hazards associated with the manufacturing of noodles have not been well characterized in Taiwan. This is an issue that flour workers can be exposed to bioaerosols (airborne fungi and bacteria) resulting flour-induced occupational asthma or allergic diseases. This study is to survey the species and concentrations of bioaerosols at different sites within a noodle factory for one year, and to investigate the effects of environmental factors on concentrations of bioaerosols. Air samples were taken twice a day, one day each month using a MAS-100 bioaerosol sampler.Nine species of culturable fungi were identified, with the main airborne fungi being Cladosporium, Penicillium, Aspergillus spp., non-sporing isolates and yeasts. Cladosporium, Penicillium and Aspergillus were the dominant fungal isolates in the indoor and outdoor air samples. Micrococcus spp. and Staphylococcus xylosus were the dominant bacterial isolates. Peak fungal and bacterial concentrations occurred at the crushing site, with mean values of 3082 and 12,616 CFU/m³. Meanwhile, the most prevalent fungi and bacteria at the crushing site were in ranges of 2.1-1.1 μm and 1.1-0.65 μm, respectively. Significant seasonal differences in total bacterial concentration were observed at all sampling sites (?P < 0.05). Moreover, significant seasonal differences were observed for most of the fungal genera except Fusarium. Levels of Aspergillus and Rhizopus differed significantly during the two sampling times, as did levels of Micrococcus spp. and Staphylococcus arlettae.Regarding the same operation procedures, relative humidity affected fungi levels more than temperature did. However, crushing generated the highest concentration of bioaerosols among all operation procedures. Furthermore, levels of bacteria at sites fitted with ventilation systems were lower than at sites without ventilation systems, especially at the crushing site. Therefore, we recommend these workers at the crushing site wear breathing protection and improve the local ventilation systems to minimize the biological hazards.     

The spatial and temporal variations in PM10 mass from six UK homes

People spend the majority of their time indoors mostly in the domestic environment, where their health may be effected by significant airborne particulate pollution. The indoor/outdoor air quality at six homes in Wales and Cornwall was investigated, based on different locations (urban, suburban, rural) and household characteristics (smokers, non-smokers). The spatial and temporal variations in PM10 mass were monitored for a calendar year, including ambient weather conditions. The activities of individuals within a household were also recorded. Monitoring of PM10 took place inside (kitchen, living room, bedroom) homes, along with concomitant collections outdoors. Samples were subjected to gravimetric analysis to determine PM10 concentrations and examined by scanning electron microscopy to identify the types of particles present on the filters. The results of the study show there are greater masses of PM10 indoors, and that the composition of the indoor PM10 is controlled by outdoor sources, and to a lesser extent by indoor anthropogenic activities, except in the presence of tobacco smokers. The indoor and outdoor PM10 collected was characterised as being a heterogeneous mixture of particles (soot, fibres, sea salt, smelter, gypsum, pollen and fungal spores).     

Assessment of the aerosolization potential for fungal spores in moldy homes

The airborne fungal concentration measured with air samplers during specific time intervals may not adequately represent the indoor air quality because of the sporadic nature of spore release from sources. The conventional source evaluation (e.g. swab and tape sampling) characterizes the mold source but does not relate to the fraction of spores that can be aerosolized from a contaminated material. As an alternative to these methods, we have recently developed and laboratory-tested a novel Fungal Spore Source Strength Tester (FSSST). It allows assessing the potential of aerosolization of fungal spores from contaminated surfaces under the most favorable release conditions. In this study, the FSSST was used to characterize the release of spores from four building materials in mold-problem homes. The spores of different species were efficiently aerosolized by the FSSST, exhibiting a total spore release rate ranging approximately from 10(2) to 10(3) cm2/min. For all tested materials, <2% of the spores on the contaminated surface were released during the tests. The airborne spore concentration estimated from the release rate data was found in most cases to be significantly greater than the concentration actually measured in these environments with simultaneous air sampling. The results suggest that the FSSST can be used for the assessment of maximum potential exposure to airborne spores released from identified sources in homes. PRACTICAL IMPLICATIONS: A recently developed FSSST was found to be suitable to measure the aerosolization potential of indoor fungal sources at the most favorable release conditions. The FSSST generates the data that allows assessing the strength of mold sources in homes with respect to their maximum ability to contaminate indoor air with fungi. The novel approach bridges two conventional methods, the air sampling and the direct source evaluation (e.g. swab sampling), thus providing a better representation of the airborne fungal exposure than these methods individually. The device prototype can be used for evaluating the effectiveness of environmental interventions by taking samples before and after the intervention. As a broader application, the FSSST can be utilized for assessing the release of various hazardous biological and non-biological particles from contaminated surfaces.     

Coarse particulate matter and airborne endotoxin within wood stove homes

Emissions from indoor biomass burning are a major public health concern in developing areas of the world. Less is known about indoor air quality, particularly airborne endotoxin, in homes burning biomass fuel in residential wood stoves in higher income countries. A filter‐based sampler was used to evaluate wintertime indoor coarse particulate matter (PM_10‐2.5) and airborne endotoxin (EU/m³, EU/mg) concentrations in 50 homes using wood stoves as their primary source of heat in western Montana. We investigated number of residents, number of pets, dampness (humidity), and frequency of wood stove usage as potential predictors of indoor airborne endotoxin concentrations. Two 48‐h sampling events per home revealed a mean winter PM_10‐2.5 concentration (± s.d.) of 12.9 (± 8.6) μg/m³, while PM_2.5 concentrations averaged 32.3 (± 32.6) μg/m³. Endotoxin concentrations measured from PM_10‐2.5 filter samples were 9.2 (± 12.4) EU/m³ and 1010 (± 1524) EU/mg. PM_10‐2.5 and PM_2.5 were significantly correlated in wood stove homes (r = 0.36, P < 0.05). The presence of pets in the homes was associated with PM_10‐2.5 but not with endotoxin concentrations. Importantly, none of the other measured home characteristics was a strong predictor of airborne endotoxin, including frequency of residential wood stove usage.     

建筑室内外空气真菌浓度相关性案例测试分析

选取某高校学生办公室进行室内外空气真菌浓度相关性和粒径的研究。结果表明:室内空气真菌浓度变化范围为1698~4429 cfu/m³,最大值出现在12:00;室外浓度范围为3569~29452 cfu/m³,最大值也出现在12:00。室内外空气真菌浓度比值均小于1,Spearman相关性分析显示室内外空气真菌呈显著正相关,且线性回归分析表明室外空气真菌是室内空气真菌的显著影响因子,可推断本研究的室外空气真菌是室内的主要来源。室内空气真菌浓度与室内人数呈显著正相关。室内外空气真菌均从Ⅰ级到Ⅳ级逐渐增加,而后Ⅴ级到Ⅵ级逐渐减小,最大值出现在第Ⅳ级,可进入人体下呼吸道的室内外空气真菌粒径占比达85.0%以上。     

Real-time measurements of PM2.5 and ozone to assess the effectiveness of residential indoor air filtration in Shanghai homes

Portable air cleaners are increasingly used in polluted areas in an attempt to reduce human exposure; however, there has been limited work characterizing their effectiveness at reducing exposure. With this in mind, we recruited forty-three children with asthma from suburban Shanghai and deployed air cleaners (with HEPA and activated carbon filters) in their bedrooms. During both 2-week filtration and non-filtration periods, low-cost PM_2.5 and O₃ air monitors were used to measure pollutants indoors, outdoors, and for personal exposure. Indoor PM_2.5 concentrations were reduced substantially with the use of air cleaners, from 34 ± 17 to 10 ± 8 µg/m³, with roughly 80% of indoor PM_2.5 estimated to come from outdoor sources. Personal exposure to PM_2.5 was reduced from 40 ± 17 to 25 ± 14 µg/m³. The more modest reductions in personal exposure and high contribution of outdoor PM_2.5 to indoor concentrations highlight the need to reduce outdoor PM_2.5 and/or to clean indoor air in multiple locations. Indoor O₃ concentrations were generally low (mean = 8±4 ppb), and no significant difference was seen by filtration status. The concentrations of pollutants and the air cleaner effectiveness were highly variable over time and across homes, highlighting the usefulness of real-time air monitors for understanding individual exposure reduction strategies.     

Fungal extracellular polysaccharides, beta (1-->3)-glucans and culturable fungi in repeated sampling of house dust

Fungal exposure inside homes has been associated with adverse respiratory symptoms in children and adults. While fungal assessment has traditionally relied upon questionnaires, fungal growth on culture plates and spore counts, new immunoassays for extracellular polysaccharides (EPS) and beta (1-->3)-glucans have enabled quantitation of fungal agents in house dust in a more timely and cost-effective manner, possibly providing a better measure of fungal exposure. We investigated associations among measurements of EPS, beta (1-->3)-glucans and culturable fungi obtained from 23 Dutch homes. From each home, dust samples were vacuumed from the living room floor twice during the Fall, Winter and Spring seasons for a total of six collections (every 6 weeks from October 1997 to May 1998). Samples were sieved and fine dust was analyzed for EPS from Aspergillus and Penicillium spp. combined, beta (1-->3)-glucans and culturable fungi. EPS was positively associated with glucan; an increase from the 25th to the 75th percentile of glucan concentration was associated with a 1.6-fold increase in EPS concentration (95% CI = 1.3 to 2.0; p < 0.01). The most significant variables associated with EPS and glucan concentrations were the surface type that was vacuumed and the concentration of total culturable fungi (in colony forming units (CFU)/g dust), with an increase in CFU/g from the 25th to the 75th percentile associated with a 1.3 (1.1-1.6)-fold increase in glucan and a 1.7 (1.3-2.2)-fold increase in EPS concentrations. In addition, the within-home variation of EPS levels were smaller than those between homes (25,646 U/g vs. 50,635 U/g), whereas the variation of glucan levels was similar within and between homes (1,300 vs. 1,205 micrograms/g). These positive associations suggest that house dust concentrations of beta (1-->3)-glucan, and particularly those of EPS, are good markers for the overall levels of fungal concentrations in floor dust which is a surrogate for estimating airborne fungal exposure.